As backlight units for liquid crystal displays etc., there are backlight units of edge light type in which a light source is disposed along at least one end portion of a light conducting plate. In such backlight units, on a light projecting surface of the light conducting plate, a light diffusing film is laminated in order to make lights emitted from the light source uniform, and an optical member such as a prism sheet is laminated in order to increase brightness for the frontal direction (Patent document 1).
In recent years, in order to make backlight units thinner, number of optical members constituting the backlight units is reduced, or optical members constituting the backlight units such as light conducting plate and others are made thinner.
However, there arises a problem that if a conventional light diffusing film is used with a light conducting plate made thinner in order to attain thinner shape, brightness for the frontal direction of the backlight unit is reduced.    Patent document 1: Japanese Patent Unexamined Publication (KOKAI) No. 9-127314 (claim 1, paragraph 0034)